Field drawings/sketches are allowed on iNat, though they should be made in the field and not from memory.
This is not correct - iNat explicitly allows/encourages photos of all of the types of evidence given above as evidenced by the documentation
“An observation records an encounter with an individual organism, or recent evidence of an organism, at a particular time and location. This includes encounters with signs of organisms like tracks, nests, scat, or things that just died.”
The issue with spectrograms is that they are not photographs, which iNat operates under the assumptions that graphics files are. Photographs are representations of visual (optic) experience/information. Spectrograms are visual representations of auditory (sonic) experience/information which is something fundamentally different.
Habitat photos are also discouraged by staff. You can see previous threads on the forum addressing this and ways to appropriately include habitat information (eg, a habitat photo which includes the organism):
https://forum.inaturalist.org/t/policy-recommendation-about-habitat-photos/10866/5
https://forum.inaturalist.org/t/is-adding-photos-of-the-nearby-habitat-inside-the-observation-of-an-organism-ok-if-the-habitat-photo-doesnt-showcase-the-organism-at-all/59680/22
https://forum.inaturalist.org/t/habitat-shots-acceptable-with-audio-observations/26630
Both spectrograms and habitat photos are officially “not encouraged” in iNat’s documentation:
https://help.inaturalist.org/en/support/solutions/articles/151000171680-what-do-i-do-if-the-observation-has-multiple-photos-depicting-different-species